The Apparently Unreactive Substrate Facilitates the Electron Transfer for Dioxygen Activation in Rieske Dioxygenases

Rieske dioxygenases belong to the non-heme iron family of oxygenases and catalyze important cis-dihydroxylation as well as O-/N-dealkylation and oxidative cyclization reactions for a wide range of substrates. The lack of substrate coordination at the non-heme ferrous iron center, however, makes it particularly challenging to delineate the role of the substrate for productive activation. Here, we studied the role of the substrate in the key elementary reaction leading to activation from a theoretical perspective by systematically considering (i) the 6-coordinate to 5-coordinate conversion of the non-heme Fe^II upon abstraction of a water ligand, (ii) binding of , and (iii) transfer of an electron from the Rieske cluster. We systematically evaluated the spin-state-dependent reaction energies and structural effects at the active site for all combinations of the three elementary processes in the presence and absence of substrate using naphthalene dioxygenase as a prototypical Rieske dioxygenase. We find that reaction energies for the generation of a coordination vacancy at the non-heme Fe center through thermoneutral H₂O reorientation and exothermic binding prior to Rieske cluster oxidation are largely insensitive to the presence of naphthalene and do not lead to formation of any of the known reactive Fe-oxygen species. By contrast, the role of the substrate becomes evident after Rieske cluster oxidation and exclusively for the 6-coordinate non-heme Fe sites in that the additional electron is found at the substrate instead of at the iron and oxygen atoms. Our results imply an allosteric control of the substrate on Rieske dioxygenase reactivity to happen prior to changes at the non-heme Fe in agreement with a strategy that avoids unproductive activation.     

Influence of media and homoconjugate pairing on transition metal hydride protonation. An IR and DFT study on proton transfer to CpRuH(CO)(PCy3)

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy(3)) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF(3))(3)COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (eta(2)-H(2))-complex 3 (DeltaH() = 11.0 +/- 0.5 kcal/mol and DeltaS() = -19 +/- 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF(3)COOH and (CF(3))(3)COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR](-) in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy(3))(eta(2)-H(2))](+) is driven by the formation of the homoconjugated anionic complex [ROHOR](-). Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy(3)), observed at temperatures above 250 K.     

Thermal gelation of cellulose in a NaOH/thiourea aqueous solution

Utilizing a novel solvent of cellulose, 6 wt % NaOH/5 wt % thiourea aqueous solution, for the first time, we prepared the thermally induced cellulose gel. We investigated the thermal gelation of cellulose solutions with rheometry and the structure of the gel with 13C NMR, wide-angle X-ray diffraction, environmental scanning electron microscopy, and atomic force microscopy. The cellulose solutions revealed an increase in both the storage modulus (G') and the loss modulus (G") with an increase in the temperature during gelation. The temperature at the turning point, where G' overrides G" because of the onset of gelation, decreased from 38.6 to 20.1 degrees C with an increase of cellulose concentration from 4 to 6 wt %. Given enough time, G' of all solutions can exceed G" at a certain temperature slightly lower than the gelation temperature, indicating that the occurrence of the gelation is also a function of time. Each of the assigned peaks of NMR of the cellulose gel is similar to that of the cellulose solution, suggesting that the gelation resulted from a physical cross-linking. The gels were composed of relatively stable network units with an average diameter of about 47 nm. At either a higher temperature (at 60 degrees C for 30 s) or a longer gelation time (at 30 degrees C for 157 s), the gel in the 5 wt % cellulose solution could form. A schematic gelation process was proposed to illustrate the sol-gel transition: the random self-association of the cellulose chains having the exposed hydroxyl in the aqueous solution promotes the physical cross-linking networks.     

A New and Simply Available Class of Hydrosoluble Bioconjugates by Coupling Paclitaxel to Hyaluronic Acid through a 4‐Hydroxybutanoic Acid Derived Linker

A simple preparation of a new hydrosoluble paclitaxel bioconjugate 8 , representing a new class of paclitaxel derivatives, is described. Bioconjugate 8 was obtained by coupling hyaluronic acid ( 2 ) to paclitaxel ( 1 ) by means of a 4‐hydroxybutanoic acid derived linker (Scheme 2).     

Mass spectrometry in the study of anthocyanins and their derivatives: differentiation of Vitis vinifera and hybrid grapes by liquid chromatography/electrospray ionization mass spectrometry and tandem mass spectrometry

A mass spectrometric-based procedure for anthocyanin profiling was set up to distinguish authentic Vitis vinifera from hybrid red grapevine cultivars. 3-O-Monoglucoside and the related acetyl-, p-coumaryl- and caffeoyl-monoglucoside anthocyanins occurred only in Vitis vinifera, whereas 3,5-O-diglucoside and the substituted acetyl-, p-coumaryl-, feruloyl- and caffeoyl-diglucoside anthocyanins were the additional pigments in hybrid grapevines. The procedure was applied expressly to identify red grape cultivars based on the anthocyanin chemo-type determination. In particular, a red grape cultivar, having 3,5-O-diglucoside anthocyanins and a novel class of anthocyanin monoglucosides, such as cyanidin-3-O-, cyanidin-3-O-(6-O-acetyl)- and cyanidin-3-O-(6-O-p-coumaryl)pentoside, was classified as hybrid. A second vine cultivar, characterized exclusively by 3-O-monoglucoside anthocyanins, was included among the Vitis vinifera species. Anthocyanin profiling by mass spectrometry could represent the core of a chemotaxonomic procedure for distinguishing American and European grapevines based on the identification of post-synthetic anthocyanidin modification.     

微波消解电感耦合等离子体发射光谱法测定塑料中铅和镉

采用微波消解技术溶样，ICP-AES法测定了塑料中的铅和镉。通过对消解试剂和微波温度程序的研究，建立了塑料样品的微波消解方法。该方法与传统马弗炉高温灰化消解方法比较，具有准确、简便、快速、省试剂、污染少、消解完全等优点。方法回收率为93％～106％，相对标准偏差(n=7)均小于2％。实际样品对比分析结果表明，方法具有良好的准确度，适于多种塑料材料中铅和镉的快速分析。     

Structure and properties of novel fibers spun from cellulose in NaOH/thiourea aqueous solution

Cellulose was dissolved rapidly in a NaOH/thiourea aqueous solution (9.5:4.5 in wt.-%) to prepare a transparent cellulose solution, which was employed, for the first time, to spin a new class of regenerated cellulose fibers by wet spinning. The structure and mechanical properties of the resulting cellulose fibers were characterized, and compared with those of commercially available viscose rayon, cuprammonium rayon and Lyocell fibers. The results from wide angle X-ray diffraction and CP/MAS 13C NMR indicated that the novel cellulose fibers have a structure typical for a family II cellulose and possessed relatively high degrees of crystallinity. Scanning electron microscopy (SEM) and optical microscopy images revealed that the cross-section of the fibers is circular, similar to natural silk. The new fibers have higher molecular weights and better mechanical properties than those of viscose rayon. This low-cost technology is simple, different from the polluting viscose process. The dissolution and regeneration of the cellulose in the NaOH/thiourea aqueous solutions were a physical process and a sol-gel transition rather than a chemical reaction, leading to the smoothness and luster of the fibers. This work provides a potential application in the field of functional fiber manufacturing.     

A simple method to optimize the HSCCC two-phase solvent system by predicting the partition coefficient for target compound

A simple method was developed to optimize the solvent ratio of the two-phase solvent system used in the high-speed counter-current chromatography (HSCCC) separation. Some mathematic equations, such as the exponential and the power equations, were established to describe the relationship between the solvent ratio and the partition coefficient. Using this new method, the two-phase solvent system was easily optimized to obtain a proper partition coefficient for the CCC separation of the target compound. Furthermore, this method was satisfactorily applied in determining the two-phase solvent system for the HSCCC preparation of pseudolaric acid B from the Chinese herb Pseudolarix kaempferi Gordon (Pinaceae). The two-phase solvent system of n-hexane/EtOAc/MeOH/H(2)O (5:5:5:5 by volume) was used with a good partition coefficient K = 1.08. As a result, 232.05 mg of pseudolaric acid B was yielded from 0.5 g of the crude extract with a purity of 97.26% by HPLC analysis.     

Three styryl‐substituted tetrahydro‐1,4‐epoxy‐1‐benzazepines: configurations,conformations and hydrogen‐bonded chains

(2SR,4RS)‐7‐Chloro‐2‐exo‐[(E)‐styryl]‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₈H₁₆ClNO, (I), crystallizes as a racemic twin in the space group P2₁ and the molecules are linked into a chain of edge‐fused R₃³(9) rings by a combination of C—H...O and C—H...N hydrogen bonds. The diastereoisomer (2RS,4RS)‐7‐chloro‐2‐endo‐[(E)‐styryl]‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, (II), also crystallizes as a racemic twin, but in the space group P2₁2₁2₁, and a two‐centre C—H...N hydrogen bond and a three‐centre C—H...(O,N) hydrogen bond combine to link the molecules into a complex chain of rings. In (2R,4R)‐7‐fluoro‐2‐endo‐[(E)‐styryl]‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₈H₁₆FNO, (III), which is not isomorphous with (II), the molecules are linked by a single C—H...O hydrogen bond into simple chains, but the molecular arrangements in (II) and (III) are nonetheless very similar. The significance of this study lies in its observation of the variations in molecular configuration and conformation, and in the variation in the supramolecular aggregation, consequent upon modest changes in the peripheral substituents.     

Surface Lewis acid-base properties of polymers measured by inverse gas chromatography

Surface Lewis acid-base properties are significant for polymers materials. The acid constant, K(a) and base constant, K(b) of many polymers were characterized by some researchers with inverse gas chromatography (IGC) in recent years. In this paper, the surface acid-base constants, K(a) and K(b) of 20 kinds of polymers measured by IGC in recent years are summarized and discussed, including seven polymers characterized in this work. After plotting K(b) versus K(a), it is found that the polymers can be encircled by a triangle. They scatter in two regions of the triangle. Four polymers exist in region I. K(b)/K(a) of the polymers in region I are 1.4-2.1. The other polymers exist in region II. Most of the polymers are relative basic materials.